Make VRF Interface and introduce additional library

[torao]

Background

Currently, we use Algorand's libsodium as the VRF library of LINE Blockchain. This is based on the next perspectives:

1. Support for ed25519 (ECVRF-ED25519-*).
2. Has a clear, free of serious infection OSS license.
3. Be efficient (but PoC shows that golang is enough performance).
4. Have been used in Algorand's production.

However, libsodium is implemented in C and requires special build procedures. Currently, it often causes build error problems when building new local or CI environments. The solution to this problem consumes a lot of time than we thought.

As you can see from the fact that the Tendermint repository contains C libraries other than libsodium, this is a problem that can eventually be solved. Given the current phases and resources, however, we shouldn't spend too much time analyzing and resolving this cause of this problem. For this reason, we'll make available alternative use of VRFs that don't cause build errors, which can be used as a substitute for libsodium in current development.

Note that this is a temporary workaround and assumes that we will eventually use libsodium or similar suitable libraries.

Goal

The goal of this work is to isolate the VRF implementation with an abstracted interface and to eliminate build errors in CI environments while providing the necessary VRF capabilities for general election behavior. The requirements with the alternative functions are as follows:

1. Support for ed25519 (ECVRF-ED25519-*).
2. Has a clear, free of serious infection OSS license.
3. Has minimum functions for use as a VRF (disregardable the security or level of perfection).
4. Successful build on local or CI environments.

It's better to be available in go get as an external library, but it's also able to be placed directly in our repository. In this case, since the directory structure is as follows (according to crypto/secp256k1), new resources may be placed in the crypto/vrf/internal/vrf/[something] directory.

There may also be work to build a CI for this additional library.